Growth of colon cancer cells, both in vitro and in vivo, has been shown to be inhibited by the active hormonal form of vitamin D, 1,25-dihydroxyvitamin D3. Unfortunately, doses of 1,25-dihydroxyvitamin D3 required to effectively treat colon tumors in vivo also stimulate the vitamin's classic effects on calcium homeostasis, resulting in the development of life-threatening hypercalcemia. Our preliminary data indicate, contrary to accepted dogma, very little 1,25-dihydroxyvitamin D3 administered either orally or injected subcutaneously actually reaches the colon to alter the transcription of target genes. We have approached these problems by synthesizing a pro-drug form of 1,25-dihydroxyvitamin D3. The pro-drug is capable of delivering high amounts of the hormone directly to the colon without substantially increasing blood concentrations of 1,25-dihydroxyvitamin D3, thus reducing the risk of a hypercalcemic response. This was achieved by conjugating a glucuronide to the hormone in a -linkage that renders it biologically inactive and resistant to mammalian digestive enzymes. Upon reaching the lower intestinal tract, however, -glucuronidase enzymes produced by resident bacterial populations cleave off the glucuronide and release the active hormone. The current proposal will determine whether using the glucuronide pro-drug system to target delivery of 1,25-dihydroxyvitamin D3 to the lower intestinal tract can slow or prevent the development of colorectal tumors without inducing systemic hypercalcemic toxicity. Chronic inflammation contributes to the development of carcinogenesis; people suffering from ulcerative colitis and Crohn's disease have an increased risk of developing colon cancer. Aim 1 will determine the efficacy of the vitamin D glucuronide pro-drug in preventing or limiting the formation and size of colon tumors induced by azoxymethane/dextran sodium sulfate in a mouse model of inflammation-associated carcinogenesis. Mutations in the adenomatous polyposis coli (Apc) gene, originally linked to familial forms of colon cancer, have also been identified in the preponderance of human colon tumors. Aim 2 will determine the effects of the glucuronide in preventing or limiting the formation and size of colon tumors in ApcMin/+ mice that carry a mutation in the mouse Apc gene and serve as a model of sporadic human colon cancer. Prior studies using 1,25-dihydroxyvitamin D3 or its analogs in the treatment of colon cancer have been limited by the development of hypercalcemia and sub-therapeutic amounts reaching the colon. The strength of the current proposal is the ability to target delivery of high concentrations of 1,25- dihydroxyvitamin D3 directly to the colon so its effects on colon carcinogenesis can be assessed in the absence of hypercalcemia.